Summary: Modeling proton mobility in acidic zeolite clusters. I. Convergence
of transition state parameters from quantum chemistry
Justin T. Fermann and Cristian Blanco
Department of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003
Scott Auerbacha)
Department of Chemistry, and Department of Chemical Engineering, University of Massachusetts, Amherst,
Massachusetts 01003
Received 30 August 1999; accepted 24 January 2000
We have applied electronic structure methods to the calculation of transition state parameters for the
O 1 O 4 proton transfer in H-Y zeolite. We arrive at a set of recommendations for calculating
these transition state parameters accurately and efficiently. Density functional theory using the
B3LYP functional and basis sets of triple- quality in the valence space, and including polarization
functions on all atoms, is the most efficient method for converging structures and vibrational
frequencies. For converging classical barrier heights, we find it necessary to augment MP2 barrier
heights calculated using large basis sets with MP4 energies obtained in more limited basis sets. We
obtain an O 1 O 4 barrier height of 86.1 kJ mol 1
, and find the curvature of the barrier at the
transition state to be 1570 cm 1
. Including long range effects from the work of Sauer et al. ACS
Symp. Ser. 721, 358 1999 results in a higher barrier, which we estimate to be 97.1 kJ mol 1